More bubkes

July 1st, 2009 by group

The “flattening of sea level since 2006” that Pielke refers to is beside the point and deceptive for several reasons (note too that Anthony Watts has extended this even further to declare that sea level from 2006 to present is actually “flat”!). First of all, trends over such a short sub-interval of a few years vary greatly due to short-term natural variations, and one could get any result one likes by cherry-picking a suitable interval (as Pielke and Lomborg both have). The absurdity of this approach is see by picking an even more recent trend, say starting in June 2007, which gives 5.3+/-2.2 mm/yr! Secondly, this short-term trend (1.6 +/- 0.9 mm/yr) is not even robust across data sets – the French analysis shown above has a trend since the beginning of 2006 of 2.9 mm/year, very similar to the long-term trend. Third, the image Pielke links to shows the data without the inverted barometer correction – the brief marked peak in late 2005, which makes the visual trend (always a poor choice of statistical methodology) almost flat since then, disappears when this effect is accounted for. This means the 2005 peak was simply due to air pressure fluctuations and has nothing to do with climatic ocean volume changes. The trend from 2006 in the data with the inverse barometer adjustment is 2.1 +/- 0.8 mm/yr.

2. Ocean heat content. The Synthesis Report states:

Current estimates indicate that ocean warming is about 50% greater than had been previously reported by the IPCC.

This is a conclusion of a revised analysis of ocean heat content data by Domingues et al., Nature 2008, and it applies to the period 1961-2003 also analysed in the IPCC report. Pielke claims this is “NOT TRUE” and counters with the claim: “There has been no statistically significant warming of the upper ocean since 2003.” But again this is not relevant to the point the Synthesis Report actually makes and again, Pielke is referring to a 5-year period which is too short to obtain statistically robust trends in the presence of short-term variability and data accuracy problems (the interannual variability for instance differs greatly between different ocean heat content data sets):

For good reasons, the Synthesis Report discusses a time span that is sufficiently long to allow meaningful comparisons. But in any case, the trend in from 2003 to 2008 in the Levitus data (the Domingues et al data does not extend past 2003), is still positive but with an uncertainty (both in the trend calculation and systematically) that makes it impossible to state whether there has been a significant change.

3. Arctic Sea Ice. The Synthesis Report states:

One of the most dramatic developments since the last IPCC Report is the rapid reduction in the area of Arctic sea ice in summer. In 2007, the minimum area covered decreased by about 2 million square kilometres as compared to previous years. In 2008, the decrease was almost as dramatic.

This decline is clearly faster than expected by models, as the following graph indicates.

Pielke’s claim that this is “NOT TRUE” is merely based on the statement that “since 2008, the anomalies have actually decreased.”